1. Field of the Invention
The present invention relates to a material having a hydrophilic surface, and more particularly to a hydrophilic material for use, for example, as glasses, mirrors, reflector plates, and protective plates, where antifogging properties and antifouling properties are required, and to a process, a coating composition and an apparatus for producing the same.
2. Background Art
When the temperature is brought to the dew point or below, the moisture in the air condenses and, consequently, fog is likely to occur on the surface of transparent materials, such as glasses and plastics, reflecting materials, such as mirrors and metal plates, and other materials, such as materials having a design on the surface thereof, Further, upon the deposition of rainwater or water spray on the surface of these materials, the water is likely to deposit as water droplets rather than as a water layer. Thus, the presence of fog or water droplets on the surface of materials often makes it impossible to exhibit functions inherent in the materials, or deteriorates the appearance and design of the materials due to scattering of light.
The following techniques are known to render the surface of the substrate hydrophilic to solve the problem of such fogging and the scattering of light.
Japanese Patent Laid-Open No. 278431/1997 discloses a method for forming profile irregularities (concaves and convexes) on the surface of a substrate, comprising the steps of: coating a surface treating agent comprising phosphoric acid or its salt, a soluble aluminum compound, a water-soluble silicate, a surfactant, and a solvent; and heat treating the coating at 300 to 700xc2x0 C.
Japanese Patent Laid-Open No. 100234/1999 discloses a method for forming profile irregularities, wherein a layer is formed which comprises metal oxide particles having a particle diameter of 3 to 300 nm and a metal oxide and has profile peaks having an arithmetic mean roughness (Ra) of 1.5 to 80 nm and a mean distance between concaves and convexes (Sm) of 4 to 300 nm.
The present inventors have now found that the regulation of the surface state of a hydrophilic material can provide a hydrophilic material having excellent antifogging properties without sacrificing the layer hardness and endurance properties.
Accordingly, it is an object of the present invention to provide a hydrophilic material which, while maintaining satisfactory layer hardness and endurance properties, is less likely to fog and is less likely to cause the deposition of water droplets and soils or stains thereon.
According to a first aspect of the present invention, there is provided a hydrophilic material comprising at least a substrate and a hydrophilic layer provided as the outermost layer on the substrate, the hydrophilic layer comprising at least hydrophilic metal oxide particles and a hydrophilic inorganic amorphous material, the hydrophilic layer having on its surface profile peaks, the hydrophilic layer having roughness properties such that, when a segment is set in only a portion not containing the profile peaks, the ten-point mean roughness (Rz) and the mean distance between concaves and convexes (Sm) obtained from a profile curve in the segment are 10 nmxe2x89xa6Rzxe2x89xa640 nm and 10 nmxe2x89xa6Smxe2x89xa6300 nm, respectively, while, when a segment is set so as to pass through the profile peaks, the ten-point mean roughness (Rz) and the mean distance between concaves and convexes (Sm) obtained from a profile curve in the segment are 40 nmxe2x89xa6Rzxe2x89xa6200 nm and 300 nmxe2x89xa6Smxe2x89xa61500 nm, respectively.
According to a second aspect of the present invention, there is provided a hydrophilic material comprising at least a substrate, a first hydrophilic layer provided on the substrate and consisting essentially of a hydrophilic inorganic amorphous material and hydrophilic metal oxide particles, and a second hydrophilic layer provided as the outermost layer on the first hydrophilic layer and consisting essentially of a hydrophilic inorganic amorphous material.